new和delete动态分配和撤销内存
一、new用法
使用new操作符时必须已知数据类型,new运算符会向系统堆区申请足够的存储空间,如果申请成功,就返回该内存块的首地址,动态分配失败,则返回一个空指针(NULL)。
new与malloc的区别:
malloc是函数,new是操作符
#include <iostream> int main() { //动态分配一个int空间 int* pp = (int*)malloc(4); //c语言写法 free(pp); int* p = new int; //C++写法 int* p1 = new int(200); //同时初始化 *p = 234; //赋值 std::cout << *p << std::endl; std::cout << *p1 << std::endl; delete p; //释放 delete p1; return 0; system("pause"); //暂停 }
#include <iostream> int main() { // 动态申请10个int空间 int* p = new int[10]; for (int i = 0; i < 10; i++) { p[i] = i + 1; std::cout << p[i] << std::endl; } int* p1 = new int[10]{ 100,101,102,103,104,105,106,107,108,109 }; //同时初始化 //需要C++11支持 for (int i = 0; i < 10; i++) { std::cout << p1[i] << std::endl; } delete p; //释放 delete[] p1; system("pause"); //暂停 }
delete注意事项
#include <iostream> int main() { int* p; //delete p; delete野指针,危险 int* p1 = NULL; delete p1; //delete空指针,安全但是无意义 system("pause"); //暂停 }